An axial fixing device for axially fixing an annular brake disk on a wheel hub of a motor vehicle, the annular brake disk having the same axis of rotation as the hub and including radial ventilation ducts regularly distributed about its periphery. According to the invention, the hub has axial guide pieces in relief, or xe2x80x9clugsxe2x80x9d, for co-operating with fluting in an inner peripheral edge of the disk to center the disk, to lock it angularly, and to guide it axially relative to the hub, each lug of the hub having a radial through channel for co-operating with a corresponding ventilation duct of the disk, and the disk is held axially in the hub with play by axial holding devices disposed between the disk and the hub.
In a motor vehicle, a brake disk is mounted on the hub of a wheel, or more generally on a bell-shaped intermediate metal part referred to as a xe2x80x9cbowlxe2x80x9d which is itself fixed to the hub. To simplify the description below, the term xe2x80x9chubxe2x80x9d is used on its own.
To connect the disk to the hub, either a fixed mount is used, or a floating mount is used.
In a fixed mount, the disk cannot move axially under thrust from the hydraulic pistons acting via the brake pads. A fixed mount suffers from numerous drawbacks, including warping of the disk due to differential expansion between the disk and the hub. This warping causes the pads to lift off the disk and constrains the driver of the motor vehicle to xe2x80x9cpumpxe2x80x9d on the brake pedal in order to bring them back into contact with the disk.
In a floating mount, as is commonly used with disks made of composite materials, the disk can move axially through a few tenths of a millimeter, thus in particular, avoiding any risk of warping.
Nevertheless, both types of mount suffer from numerous defects that restrict potential use. These comprise essentially the large number of parts necessary for transmitting the braking torque, thus giving rise to high mass and cost, and also problems associated with assembling and disassembling the brake disk and the large amount of space occupied laterally by both of those types of prior art mount.
Thus, the present invention seeks to remedy those drawbacks by means of an axial fixing device which holds the disk axially with an accurately controlled amount of play. An object of the invention is also to propose a device which can be implemented with ventilated brake disks so as to make high speed uses possible. Another object of the invention is to make a device that is simple to assemble and low in weight.
These objects are achieved by an axial fixing device for axially fixing an annular brake disk on a wheel hub of a motor vehicle, the annular brake disk having the same axis of rotation as the hub and including radial ventilation ducts regularly distributed about its periphery, wherein said hub has axial guide pieces in relief, or xe2x80x9clugsxe2x80x9d, for co-operating with fluting in an inner peripheral edge of the disk to center the disk, to lock it angularly, and to guide it axially relative to the hub, each lug of the hub having a radial through channel for co-operating with a corresponding ventilation duct of the disk, and wherein the disk is held axially in the hub with play by axial holding means disposed between the disk and the hub.
In a first embodiment, said axial holding means comprise a plurality of radial pegs, each peg being engaged firstly in a radial through channel of a lug of the hub and secondly in a radial ventilation duct facing it in the brake disk. Advantageously, the radial through channel of the lug has a diameter that is slightly greater than that of the peg so as to provide a small amount of axial play in the range 0.2 mm to 0.4 mm. Preferably, the axial holding means includes at least one peg with a radial through bore to avoid impeding internal ventilation of the disk. It further includes locking means for holding the peg in position during rotation of the wheel and thus prevent it moving radially. Said locking means may comprise a stop plate fixed on a distal face of the lug and designed to co-operate with a groove in the peg.
In a second embodiment, said axial holding means comprises at least one tab fixed on a distal face of a lug of the hub and designed to co-operate with a slot perpendicular to the common axis and formed in each of the two adjacent pieces in relief of the inner peripheral edge of the disk. Said lug of the hub further includes a groove perpendicular to the common axis and formed in line with the slot to receive the tab. Advantageously, the groove is slightly wider than the slot so as to provide a small amount of axial play in the range 0.2 mm to 0.4 mm.
The brake disk is made of a carbon/carbon composite material.